1. Field of the Invention
The present invention relates to a composite stator structure and in particular to a stator structure in a cooling fan.
2. Brief Discussion of the Related Art
FIG. 1 shows a conventional brushless DC motor. The motor comprises a magnetic sleeve 10, a first bobbin 11, a second bobbin 12, a first pole plate 13, a second pole plate 14, and a third pole plate 15. The second pole plate 14, second bobbin 12, third pole plate 15, first bobbin 11, and first pole plate 13 are sequentially tightly assembled with the magnetic sleeve 10. Protrusions 111 and 121 on the first and second bobbins 11 and 12 must be engaged with the holes 131, 141, and 151 on the first, second, and third pole plates 13, 14, and 15 respectively so as to complete the position and angle of the first, second and third pole plates 13, 14, and 15. However, the first and second bobbins 11 and 12 are made of plastic, and the first, second and third pole plates 13, 14 and 15 are tightly telescoped to the magnetic sleeve 10, they are uneasily pressed to the precise angle and depth, thereby causing the inconvenience of the manufacturing process. Further, the magnetic sleeve 10 can not be formed by punching in one time, which must be turned off inwardly and outwardly so that it will increase the difficulty and cost of manufacturing process. Moreover, the material of the magnetic sleeve 10 is different from those of the first, second, and third pole plates 13, 14, and 15 such that it will increase the magnetic resistance and a lot of heat and easily cause the residually magnetic phenomenon and worse magnetic loop.